1 | /* SPDX-License-Identifier: GPL-2.0 */ |
2 | #ifndef _LINUX_FORTIFY_STRING_H_ |
3 | #define _LINUX_FORTIFY_STRING_H_ |
4 | |
5 | #include <linux/bitfield.h> |
6 | #include <linux/bug.h> |
7 | #include <linux/const.h> |
8 | #include <linux/limits.h> |
9 | |
10 | #define __FORTIFY_INLINE extern __always_inline __gnu_inline __overloadable |
11 | #define __RENAME(x) __asm__(#x) |
12 | |
13 | #define FORTIFY_REASON_DIR(r) FIELD_GET(BIT(0), r) |
14 | #define FORTIFY_REASON_FUNC(r) FIELD_GET(GENMASK(7, 1), r) |
15 | #define FORTIFY_REASON(func, write) (FIELD_PREP(BIT(0), write) | \ |
16 | FIELD_PREP(GENMASK(7, 1), func)) |
17 | |
18 | #ifndef fortify_panic |
19 | # define fortify_panic(func, write, avail, size, retfail) \ |
20 | __fortify_panic(FORTIFY_REASON(func, write), avail, size) |
21 | #endif |
22 | |
23 | #define FORTIFY_READ 0 |
24 | #define FORTIFY_WRITE 1 |
25 | |
26 | #define EACH_FORTIFY_FUNC(macro) \ |
27 | macro(strncpy), \ |
28 | macro(strnlen), \ |
29 | macro(strlen), \ |
30 | macro(strscpy), \ |
31 | macro(strlcat), \ |
32 | macro(strcat), \ |
33 | macro(strncat), \ |
34 | macro(memset), \ |
35 | macro(memcpy), \ |
36 | macro(memmove), \ |
37 | macro(memscan), \ |
38 | macro(memcmp), \ |
39 | macro(memchr), \ |
40 | macro(memchr_inv), \ |
41 | macro(kmemdup), \ |
42 | macro(strcpy), \ |
43 | macro(UNKNOWN), |
44 | |
45 | #define MAKE_FORTIFY_FUNC(func) FORTIFY_FUNC_##func |
46 | |
47 | enum fortify_func { |
48 | EACH_FORTIFY_FUNC(MAKE_FORTIFY_FUNC) |
49 | }; |
50 | |
51 | void __fortify_report(const u8 reason, const size_t avail, const size_t size); |
52 | void __fortify_panic(const u8 reason, const size_t avail, const size_t size) __cold __noreturn; |
53 | void __read_overflow(void) __compiletime_error("detected read beyond size of object (1st parameter)" ); |
54 | void __read_overflow2(void) __compiletime_error("detected read beyond size of object (2nd parameter)" ); |
55 | void __read_overflow2_field(size_t avail, size_t wanted) __compiletime_warning("detected read beyond size of field (2nd parameter); maybe use struct_group()?" ); |
56 | void __write_overflow(void) __compiletime_error("detected write beyond size of object (1st parameter)" ); |
57 | void __write_overflow_field(size_t avail, size_t wanted) __compiletime_warning("detected write beyond size of field (1st parameter); maybe use struct_group()?" ); |
58 | |
59 | #define __compiletime_strlen(p) \ |
60 | ({ \ |
61 | char *__p = (char *)(p); \ |
62 | size_t __ret = SIZE_MAX; \ |
63 | const size_t __p_size = __member_size(p); \ |
64 | if (__p_size != SIZE_MAX && \ |
65 | __builtin_constant_p(*__p)) { \ |
66 | size_t __p_len = __p_size - 1; \ |
67 | if (__builtin_constant_p(__p[__p_len]) && \ |
68 | __p[__p_len] == '\0') \ |
69 | __ret = __builtin_strlen(__p); \ |
70 | } \ |
71 | __ret; \ |
72 | }) |
73 | |
74 | #if defined(CONFIG_KASAN_GENERIC) || defined(CONFIG_KASAN_SW_TAGS) |
75 | extern void *__underlying_memchr(const void *p, int c, __kernel_size_t size) __RENAME(memchr); |
76 | extern int __underlying_memcmp(const void *p, const void *q, __kernel_size_t size) __RENAME(memcmp); |
77 | extern void *__underlying_memcpy(void *p, const void *q, __kernel_size_t size) __RENAME(memcpy); |
78 | extern void *__underlying_memmove(void *p, const void *q, __kernel_size_t size) __RENAME(memmove); |
79 | extern void *__underlying_memset(void *p, int c, __kernel_size_t size) __RENAME(memset); |
80 | extern char *__underlying_strcat(char *p, const char *q) __RENAME(strcat); |
81 | extern char *__underlying_strcpy(char *p, const char *q) __RENAME(strcpy); |
82 | extern __kernel_size_t __underlying_strlen(const char *p) __RENAME(strlen); |
83 | extern char *__underlying_strncat(char *p, const char *q, __kernel_size_t count) __RENAME(strncat); |
84 | extern char *__underlying_strncpy(char *p, const char *q, __kernel_size_t size) __RENAME(strncpy); |
85 | #else |
86 | |
87 | #if defined(__SANITIZE_MEMORY__) |
88 | /* |
89 | * For KMSAN builds all memcpy/memset/memmove calls should be replaced by the |
90 | * corresponding __msan_XXX functions. |
91 | */ |
92 | #include <linux/kmsan_string.h> |
93 | #define __underlying_memcpy __msan_memcpy |
94 | #define __underlying_memmove __msan_memmove |
95 | #define __underlying_memset __msan_memset |
96 | #else |
97 | #define __underlying_memcpy __builtin_memcpy |
98 | #define __underlying_memmove __builtin_memmove |
99 | #define __underlying_memset __builtin_memset |
100 | #endif |
101 | |
102 | #define __underlying_memchr __builtin_memchr |
103 | #define __underlying_memcmp __builtin_memcmp |
104 | #define __underlying_strcat __builtin_strcat |
105 | #define __underlying_strcpy __builtin_strcpy |
106 | #define __underlying_strlen __builtin_strlen |
107 | #define __underlying_strncat __builtin_strncat |
108 | #define __underlying_strncpy __builtin_strncpy |
109 | #endif |
110 | |
111 | /** |
112 | * unsafe_memcpy - memcpy implementation with no FORTIFY bounds checking |
113 | * |
114 | * @dst: Destination memory address to write to |
115 | * @src: Source memory address to read from |
116 | * @bytes: How many bytes to write to @dst from @src |
117 | * @justification: Free-form text or comment describing why the use is needed |
118 | * |
119 | * This should be used for corner cases where the compiler cannot do the |
120 | * right thing, or during transitions between APIs, etc. It should be used |
121 | * very rarely, and includes a place for justification detailing where bounds |
122 | * checking has happened, and why existing solutions cannot be employed. |
123 | */ |
124 | #define unsafe_memcpy(dst, src, bytes, justification) \ |
125 | __underlying_memcpy(dst, src, bytes) |
126 | |
127 | /* |
128 | * Clang's use of __builtin_*object_size() within inlines needs hinting via |
129 | * __pass_*object_size(). The preference is to only ever use type 1 (member |
130 | * size, rather than struct size), but there remain some stragglers using |
131 | * type 0 that will be converted in the future. |
132 | */ |
133 | #if __has_builtin(__builtin_dynamic_object_size) |
134 | #define POS __pass_dynamic_object_size(1) |
135 | #define POS0 __pass_dynamic_object_size(0) |
136 | #else |
137 | #define POS __pass_object_size(1) |
138 | #define POS0 __pass_object_size(0) |
139 | #endif |
140 | |
141 | #define __compiletime_lessthan(bounds, length) ( \ |
142 | __builtin_constant_p((bounds) < (length)) && \ |
143 | (bounds) < (length) \ |
144 | ) |
145 | |
146 | /** |
147 | * strncpy - Copy a string to memory with non-guaranteed NUL padding |
148 | * |
149 | * @p: pointer to destination of copy |
150 | * @q: pointer to NUL-terminated source string to copy |
151 | * @size: bytes to write at @p |
152 | * |
153 | * If strlen(@q) >= @size, the copy of @q will stop after @size bytes, |
154 | * and @p will NOT be NUL-terminated |
155 | * |
156 | * If strlen(@q) < @size, following the copy of @q, trailing NUL bytes |
157 | * will be written to @p until @size total bytes have been written. |
158 | * |
159 | * Do not use this function. While FORTIFY_SOURCE tries to avoid |
160 | * over-reads of @q, it cannot defend against writing unterminated |
161 | * results to @p. Using strncpy() remains ambiguous and fragile. |
162 | * Instead, please choose an alternative, so that the expectation |
163 | * of @p's contents is unambiguous: |
164 | * |
165 | * +--------------------+--------------------+------------+ |
166 | * | **p** needs to be: | padded to **size** | not padded | |
167 | * +====================+====================+============+ |
168 | * | NUL-terminated | strscpy_pad() | strscpy() | |
169 | * +--------------------+--------------------+------------+ |
170 | * | not NUL-terminated | strtomem_pad() | strtomem() | |
171 | * +--------------------+--------------------+------------+ |
172 | * |
173 | * Note strscpy*()'s differing return values for detecting truncation, |
174 | * and strtomem*()'s expectation that the destination is marked with |
175 | * __nonstring when it is a character array. |
176 | * |
177 | */ |
178 | __FORTIFY_INLINE __diagnose_as(__builtin_strncpy, 1, 2, 3) |
179 | char *strncpy(char * const POS p, const char *q, __kernel_size_t size) |
180 | { |
181 | const size_t p_size = __member_size(p); |
182 | |
183 | if (__compiletime_lessthan(p_size, size)) |
184 | __write_overflow(); |
185 | if (p_size < size) |
186 | fortify_panic(FORTIFY_FUNC_strncpy, FORTIFY_WRITE, p_size, size, p); |
187 | return __underlying_strncpy(p, q, size); |
188 | } |
189 | |
190 | extern __kernel_size_t __real_strnlen(const char *, __kernel_size_t) __RENAME(strnlen); |
191 | /** |
192 | * strnlen - Return bounded count of characters in a NUL-terminated string |
193 | * |
194 | * @p: pointer to NUL-terminated string to count. |
195 | * @maxlen: maximum number of characters to count. |
196 | * |
197 | * Returns number of characters in @p (NOT including the final NUL), or |
198 | * @maxlen, if no NUL has been found up to there. |
199 | * |
200 | */ |
201 | __FORTIFY_INLINE __kernel_size_t strnlen(const char * const POS p, __kernel_size_t maxlen) |
202 | { |
203 | const size_t p_size = __member_size(p); |
204 | const size_t p_len = __compiletime_strlen(p); |
205 | size_t ret; |
206 | |
207 | /* We can take compile-time actions when maxlen is const. */ |
208 | if (__builtin_constant_p(maxlen) && p_len != SIZE_MAX) { |
209 | /* If p is const, we can use its compile-time-known len. */ |
210 | if (maxlen >= p_size) |
211 | return p_len; |
212 | } |
213 | |
214 | /* Do not check characters beyond the end of p. */ |
215 | ret = __real_strnlen(p, maxlen < p_size ? maxlen : p_size); |
216 | if (p_size <= ret && maxlen != ret) |
217 | fortify_panic(FORTIFY_FUNC_strnlen, FORTIFY_READ, p_size, ret + 1, ret); |
218 | return ret; |
219 | } |
220 | |
221 | /* |
222 | * Defined after fortified strnlen to reuse it. However, it must still be |
223 | * possible for strlen() to be used on compile-time strings for use in |
224 | * static initializers (i.e. as a constant expression). |
225 | */ |
226 | /** |
227 | * strlen - Return count of characters in a NUL-terminated string |
228 | * |
229 | * @p: pointer to NUL-terminated string to count. |
230 | * |
231 | * Do not use this function unless the string length is known at |
232 | * compile-time. When @p is unterminated, this function may crash |
233 | * or return unexpected counts that could lead to memory content |
234 | * exposures. Prefer strnlen(). |
235 | * |
236 | * Returns number of characters in @p (NOT including the final NUL). |
237 | * |
238 | */ |
239 | #define strlen(p) \ |
240 | __builtin_choose_expr(__is_constexpr(__builtin_strlen(p)), \ |
241 | __builtin_strlen(p), __fortify_strlen(p)) |
242 | __FORTIFY_INLINE __diagnose_as(__builtin_strlen, 1) |
243 | __kernel_size_t __fortify_strlen(const char * const POS p) |
244 | { |
245 | const size_t p_size = __member_size(p); |
246 | __kernel_size_t ret; |
247 | |
248 | /* Give up if we don't know how large p is. */ |
249 | if (p_size == SIZE_MAX) |
250 | return __underlying_strlen(p); |
251 | ret = strnlen(p, maxlen: p_size); |
252 | if (p_size <= ret) |
253 | fortify_panic(FORTIFY_FUNC_strlen, FORTIFY_READ, p_size, ret + 1, ret); |
254 | return ret; |
255 | } |
256 | |
257 | /* Defined after fortified strnlen() to reuse it. */ |
258 | extern ssize_t __real_strscpy(char *, const char *, size_t) __RENAME(sized_strscpy); |
259 | __FORTIFY_INLINE ssize_t sized_strscpy(char * const POS p, const char * const POS q, size_t size) |
260 | { |
261 | /* Use string size rather than possible enclosing struct size. */ |
262 | const size_t p_size = __member_size(p); |
263 | const size_t q_size = __member_size(q); |
264 | size_t len; |
265 | |
266 | /* If we cannot get size of p and q default to call strscpy. */ |
267 | if (p_size == SIZE_MAX && q_size == SIZE_MAX) |
268 | return __real_strscpy(p, q, size); |
269 | |
270 | /* |
271 | * If size can be known at compile time and is greater than |
272 | * p_size, generate a compile time write overflow error. |
273 | */ |
274 | if (__compiletime_lessthan(p_size, size)) |
275 | __write_overflow(); |
276 | |
277 | /* Short-circuit for compile-time known-safe lengths. */ |
278 | if (__compiletime_lessthan(p_size, SIZE_MAX)) { |
279 | len = __compiletime_strlen(q); |
280 | |
281 | if (len < SIZE_MAX && __compiletime_lessthan(len, size)) { |
282 | __underlying_memcpy(p, q, len + 1); |
283 | return len; |
284 | } |
285 | } |
286 | |
287 | /* |
288 | * This call protects from read overflow, because len will default to q |
289 | * length if it smaller than size. |
290 | */ |
291 | len = strnlen(p: q, maxlen: size); |
292 | /* |
293 | * If len equals size, we will copy only size bytes which leads to |
294 | * -E2BIG being returned. |
295 | * Otherwise we will copy len + 1 because of the final '\O'. |
296 | */ |
297 | len = len == size ? size : len + 1; |
298 | |
299 | /* |
300 | * Generate a runtime write overflow error if len is greater than |
301 | * p_size. |
302 | */ |
303 | if (p_size < len) |
304 | fortify_panic(FORTIFY_FUNC_strscpy, FORTIFY_WRITE, p_size, len, -E2BIG); |
305 | |
306 | /* |
307 | * We can now safely call vanilla strscpy because we are protected from: |
308 | * 1. Read overflow thanks to call to strnlen(). |
309 | * 2. Write overflow thanks to above ifs. |
310 | */ |
311 | return __real_strscpy(p, q, len); |
312 | } |
313 | |
314 | /* Defined after fortified strlen() to reuse it. */ |
315 | extern size_t __real_strlcat(char *p, const char *q, size_t avail) __RENAME(strlcat); |
316 | /** |
317 | * strlcat - Append a string to an existing string |
318 | * |
319 | * @p: pointer to %NUL-terminated string to append to |
320 | * @q: pointer to %NUL-terminated string to append from |
321 | * @avail: Maximum bytes available in @p |
322 | * |
323 | * Appends %NUL-terminated string @q after the %NUL-terminated |
324 | * string at @p, but will not write beyond @avail bytes total, |
325 | * potentially truncating the copy from @q. @p will stay |
326 | * %NUL-terminated only if a %NUL already existed within |
327 | * the @avail bytes of @p. If so, the resulting number of |
328 | * bytes copied from @q will be at most "@avail - strlen(@p) - 1". |
329 | * |
330 | * Do not use this function. While FORTIFY_SOURCE tries to avoid |
331 | * read and write overflows, this is only possible when the sizes |
332 | * of @p and @q are known to the compiler. Prefer building the |
333 | * string with formatting, via scnprintf(), seq_buf, or similar. |
334 | * |
335 | * Returns total bytes that _would_ have been contained by @p |
336 | * regardless of truncation, similar to snprintf(). If return |
337 | * value is >= @avail, the string has been truncated. |
338 | * |
339 | */ |
340 | __FORTIFY_INLINE |
341 | size_t strlcat(char * const POS p, const char * const POS q, size_t avail) |
342 | { |
343 | const size_t p_size = __member_size(p); |
344 | const size_t q_size = __member_size(q); |
345 | size_t p_len, copy_len; |
346 | size_t actual, wanted; |
347 | |
348 | /* Give up immediately if both buffer sizes are unknown. */ |
349 | if (p_size == SIZE_MAX && q_size == SIZE_MAX) |
350 | return __real_strlcat(p, q, avail); |
351 | |
352 | p_len = strnlen(p, maxlen: avail); |
353 | copy_len = strlen(q); |
354 | wanted = actual = p_len + copy_len; |
355 | |
356 | /* Cannot append any more: report truncation. */ |
357 | if (avail <= p_len) |
358 | return wanted; |
359 | |
360 | /* Give up if string is already overflowed. */ |
361 | if (p_size <= p_len) |
362 | fortify_panic(FORTIFY_FUNC_strlcat, FORTIFY_READ, p_size, p_len + 1, wanted); |
363 | |
364 | if (actual >= avail) { |
365 | copy_len = avail - p_len - 1; |
366 | actual = p_len + copy_len; |
367 | } |
368 | |
369 | /* Give up if copy will overflow. */ |
370 | if (p_size <= actual) |
371 | fortify_panic(FORTIFY_FUNC_strlcat, FORTIFY_WRITE, p_size, actual + 1, wanted); |
372 | __underlying_memcpy(p + p_len, q, copy_len); |
373 | p[actual] = '\0'; |
374 | |
375 | return wanted; |
376 | } |
377 | |
378 | /* Defined after fortified strlcat() to reuse it. */ |
379 | /** |
380 | * strcat - Append a string to an existing string |
381 | * |
382 | * @p: pointer to NUL-terminated string to append to |
383 | * @q: pointer to NUL-terminated source string to append from |
384 | * |
385 | * Do not use this function. While FORTIFY_SOURCE tries to avoid |
386 | * read and write overflows, this is only possible when the |
387 | * destination buffer size is known to the compiler. Prefer |
388 | * building the string with formatting, via scnprintf() or similar. |
389 | * At the very least, use strncat(). |
390 | * |
391 | * Returns @p. |
392 | * |
393 | */ |
394 | __FORTIFY_INLINE __diagnose_as(__builtin_strcat, 1, 2) |
395 | char *strcat(char * const POS p, const char *q) |
396 | { |
397 | const size_t p_size = __member_size(p); |
398 | const size_t wanted = strlcat(p, q, avail: p_size); |
399 | |
400 | if (p_size <= wanted) |
401 | fortify_panic(FORTIFY_FUNC_strcat, FORTIFY_WRITE, p_size, wanted + 1, p); |
402 | return p; |
403 | } |
404 | |
405 | /** |
406 | * strncat - Append a string to an existing string |
407 | * |
408 | * @p: pointer to NUL-terminated string to append to |
409 | * @q: pointer to source string to append from |
410 | * @count: Maximum bytes to read from @q |
411 | * |
412 | * Appends at most @count bytes from @q (stopping at the first |
413 | * NUL byte) after the NUL-terminated string at @p. @p will be |
414 | * NUL-terminated. |
415 | * |
416 | * Do not use this function. While FORTIFY_SOURCE tries to avoid |
417 | * read and write overflows, this is only possible when the sizes |
418 | * of @p and @q are known to the compiler. Prefer building the |
419 | * string with formatting, via scnprintf() or similar. |
420 | * |
421 | * Returns @p. |
422 | * |
423 | */ |
424 | /* Defined after fortified strlen() and strnlen() to reuse them. */ |
425 | __FORTIFY_INLINE __diagnose_as(__builtin_strncat, 1, 2, 3) |
426 | char *strncat(char * const POS p, const char * const POS q, __kernel_size_t count) |
427 | { |
428 | const size_t p_size = __member_size(p); |
429 | const size_t q_size = __member_size(q); |
430 | size_t p_len, copy_len, total; |
431 | |
432 | if (p_size == SIZE_MAX && q_size == SIZE_MAX) |
433 | return __underlying_strncat(p, q, count); |
434 | p_len = strlen(p); |
435 | copy_len = strnlen(p: q, maxlen: count); |
436 | total = p_len + copy_len + 1; |
437 | if (p_size < total) |
438 | fortify_panic(FORTIFY_FUNC_strncat, FORTIFY_WRITE, p_size, total, p); |
439 | __underlying_memcpy(p + p_len, q, copy_len); |
440 | p[p_len + copy_len] = '\0'; |
441 | return p; |
442 | } |
443 | |
444 | __FORTIFY_INLINE bool fortify_memset_chk(__kernel_size_t size, |
445 | const size_t p_size, |
446 | const size_t p_size_field) |
447 | { |
448 | if (__builtin_constant_p(size)) { |
449 | /* |
450 | * Length argument is a constant expression, so we |
451 | * can perform compile-time bounds checking where |
452 | * buffer sizes are also known at compile time. |
453 | */ |
454 | |
455 | /* Error when size is larger than enclosing struct. */ |
456 | if (__compiletime_lessthan(p_size_field, p_size) && |
457 | __compiletime_lessthan(p_size, size)) |
458 | __write_overflow(); |
459 | |
460 | /* Warn when write size is larger than dest field. */ |
461 | if (__compiletime_lessthan(p_size_field, size)) |
462 | __write_overflow_field(avail: p_size_field, wanted: size); |
463 | } |
464 | /* |
465 | * At this point, length argument may not be a constant expression, |
466 | * so run-time bounds checking can be done where buffer sizes are |
467 | * known. (This is not an "else" because the above checks may only |
468 | * be compile-time warnings, and we want to still warn for run-time |
469 | * overflows.) |
470 | */ |
471 | |
472 | /* |
473 | * Always stop accesses beyond the struct that contains the |
474 | * field, when the buffer's remaining size is known. |
475 | * (The SIZE_MAX test is to optimize away checks where the buffer |
476 | * lengths are unknown.) |
477 | */ |
478 | if (p_size != SIZE_MAX && p_size < size) |
479 | fortify_panic(FORTIFY_FUNC_memset, FORTIFY_WRITE, p_size, size, true); |
480 | return false; |
481 | } |
482 | |
483 | #define __fortify_memset_chk(p, c, size, p_size, p_size_field) ({ \ |
484 | size_t __fortify_size = (size_t)(size); \ |
485 | fortify_memset_chk(__fortify_size, p_size, p_size_field), \ |
486 | __underlying_memset(p, c, __fortify_size); \ |
487 | }) |
488 | |
489 | /* |
490 | * __struct_size() vs __member_size() must be captured here to avoid |
491 | * evaluating argument side-effects further into the macro layers. |
492 | */ |
493 | #ifndef CONFIG_KMSAN |
494 | #define memset(p, c, s) __fortify_memset_chk(p, c, s, \ |
495 | __struct_size(p), __member_size(p)) |
496 | #endif |
497 | |
498 | /* |
499 | * To make sure the compiler can enforce protection against buffer overflows, |
500 | * memcpy(), memmove(), and memset() must not be used beyond individual |
501 | * struct members. If you need to copy across multiple members, please use |
502 | * struct_group() to create a named mirror of an anonymous struct union. |
503 | * (e.g. see struct sk_buff.) Read overflow checking is currently only |
504 | * done when a write overflow is also present, or when building with W=1. |
505 | * |
506 | * Mitigation coverage matrix |
507 | * Bounds checking at: |
508 | * +-------+-------+-------+-------+ |
509 | * | Compile time | Run time | |
510 | * memcpy() argument sizes: | write | read | write | read | |
511 | * dest source length +-------+-------+-------+-------+ |
512 | * memcpy(known, known, constant) | y | y | n/a | n/a | |
513 | * memcpy(known, unknown, constant) | y | n | n/a | V | |
514 | * memcpy(known, known, dynamic) | n | n | B | B | |
515 | * memcpy(known, unknown, dynamic) | n | n | B | V | |
516 | * memcpy(unknown, known, constant) | n | y | V | n/a | |
517 | * memcpy(unknown, unknown, constant) | n | n | V | V | |
518 | * memcpy(unknown, known, dynamic) | n | n | V | B | |
519 | * memcpy(unknown, unknown, dynamic) | n | n | V | V | |
520 | * +-------+-------+-------+-------+ |
521 | * |
522 | * y = perform deterministic compile-time bounds checking |
523 | * n = cannot perform deterministic compile-time bounds checking |
524 | * n/a = no run-time bounds checking needed since compile-time deterministic |
525 | * B = can perform run-time bounds checking (currently unimplemented) |
526 | * V = vulnerable to run-time overflow (will need refactoring to solve) |
527 | * |
528 | */ |
529 | __FORTIFY_INLINE bool fortify_memcpy_chk(__kernel_size_t size, |
530 | const size_t p_size, |
531 | const size_t q_size, |
532 | const size_t p_size_field, |
533 | const size_t q_size_field, |
534 | const u8 func) |
535 | { |
536 | if (__builtin_constant_p(size)) { |
537 | /* |
538 | * Length argument is a constant expression, so we |
539 | * can perform compile-time bounds checking where |
540 | * buffer sizes are also known at compile time. |
541 | */ |
542 | |
543 | /* Error when size is larger than enclosing struct. */ |
544 | if (__compiletime_lessthan(p_size_field, p_size) && |
545 | __compiletime_lessthan(p_size, size)) |
546 | __write_overflow(); |
547 | if (__compiletime_lessthan(q_size_field, q_size) && |
548 | __compiletime_lessthan(q_size, size)) |
549 | __read_overflow2(); |
550 | |
551 | /* Warn when write size argument larger than dest field. */ |
552 | if (__compiletime_lessthan(p_size_field, size)) |
553 | __write_overflow_field(avail: p_size_field, wanted: size); |
554 | /* |
555 | * Warn for source field over-read when building with W=1 |
556 | * or when an over-write happened, so both can be fixed at |
557 | * the same time. |
558 | */ |
559 | if ((IS_ENABLED(KBUILD_EXTRA_WARN1) || |
560 | __compiletime_lessthan(p_size_field, size)) && |
561 | __compiletime_lessthan(q_size_field, size)) |
562 | __read_overflow2_field(avail: q_size_field, wanted: size); |
563 | } |
564 | /* |
565 | * At this point, length argument may not be a constant expression, |
566 | * so run-time bounds checking can be done where buffer sizes are |
567 | * known. (This is not an "else" because the above checks may only |
568 | * be compile-time warnings, and we want to still warn for run-time |
569 | * overflows.) |
570 | */ |
571 | |
572 | /* |
573 | * Always stop accesses beyond the struct that contains the |
574 | * field, when the buffer's remaining size is known. |
575 | * (The SIZE_MAX test is to optimize away checks where the buffer |
576 | * lengths are unknown.) |
577 | */ |
578 | if (p_size != SIZE_MAX && p_size < size) |
579 | fortify_panic(func, FORTIFY_WRITE, p_size, size, true); |
580 | else if (q_size != SIZE_MAX && q_size < size) |
581 | fortify_panic(func, FORTIFY_READ, p_size, size, true); |
582 | |
583 | /* |
584 | * Warn when writing beyond destination field size. |
585 | * |
586 | * We must ignore p_size_field == 0 for existing 0-element |
587 | * fake flexible arrays, until they are all converted to |
588 | * proper flexible arrays. |
589 | * |
590 | * The implementation of __builtin_*object_size() behaves |
591 | * like sizeof() when not directly referencing a flexible |
592 | * array member, which means there will be many bounds checks |
593 | * that will appear at run-time, without a way for them to be |
594 | * detected at compile-time (as can be done when the destination |
595 | * is specifically the flexible array member). |
596 | * https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101832 |
597 | */ |
598 | if (p_size_field != 0 && p_size_field != SIZE_MAX && |
599 | p_size != p_size_field && p_size_field < size) |
600 | return true; |
601 | |
602 | return false; |
603 | } |
604 | |
605 | #define __fortify_memcpy_chk(p, q, size, p_size, q_size, \ |
606 | p_size_field, q_size_field, op) ({ \ |
607 | const size_t __fortify_size = (size_t)(size); \ |
608 | const size_t __p_size = (p_size); \ |
609 | const size_t __q_size = (q_size); \ |
610 | const size_t __p_size_field = (p_size_field); \ |
611 | const size_t __q_size_field = (q_size_field); \ |
612 | WARN_ONCE(fortify_memcpy_chk(__fortify_size, __p_size, \ |
613 | __q_size, __p_size_field, \ |
614 | __q_size_field, FORTIFY_FUNC_ ##op), \ |
615 | #op ": detected field-spanning write (size %zu) of single %s (size %zu)\n", \ |
616 | __fortify_size, \ |
617 | "field \"" #p "\" at " FILE_LINE, \ |
618 | __p_size_field); \ |
619 | __underlying_##op(p, q, __fortify_size); \ |
620 | }) |
621 | |
622 | /* |
623 | * Notes about compile-time buffer size detection: |
624 | * |
625 | * With these types... |
626 | * |
627 | * struct middle { |
628 | * u16 a; |
629 | * u8 middle_buf[16]; |
630 | * int b; |
631 | * }; |
632 | * struct end { |
633 | * u16 a; |
634 | * u8 end_buf[16]; |
635 | * }; |
636 | * struct flex { |
637 | * int a; |
638 | * u8 flex_buf[]; |
639 | * }; |
640 | * |
641 | * void func(TYPE *ptr) { ... } |
642 | * |
643 | * Cases where destination size cannot be currently detected: |
644 | * - the size of ptr's object (seemingly by design, gcc & clang fail): |
645 | * __builtin_object_size(ptr, 1) == SIZE_MAX |
646 | * - the size of flexible arrays in ptr's obj (by design, dynamic size): |
647 | * __builtin_object_size(ptr->flex_buf, 1) == SIZE_MAX |
648 | * - the size of ANY array at the end of ptr's obj (gcc and clang bug): |
649 | * __builtin_object_size(ptr->end_buf, 1) == SIZE_MAX |
650 | * https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101836 |
651 | * |
652 | * Cases where destination size is currently detected: |
653 | * - the size of non-array members within ptr's object: |
654 | * __builtin_object_size(ptr->a, 1) == 2 |
655 | * - the size of non-flexible-array in the middle of ptr's obj: |
656 | * __builtin_object_size(ptr->middle_buf, 1) == 16 |
657 | * |
658 | */ |
659 | |
660 | /* |
661 | * __struct_size() vs __member_size() must be captured here to avoid |
662 | * evaluating argument side-effects further into the macro layers. |
663 | */ |
664 | #define memcpy(p, q, s) __fortify_memcpy_chk(p, q, s, \ |
665 | __struct_size(p), __struct_size(q), \ |
666 | __member_size(p), __member_size(q), \ |
667 | memcpy) |
668 | #define memmove(p, q, s) __fortify_memcpy_chk(p, q, s, \ |
669 | __struct_size(p), __struct_size(q), \ |
670 | __member_size(p), __member_size(q), \ |
671 | memmove) |
672 | |
673 | extern void *__real_memscan(void *, int, __kernel_size_t) __RENAME(memscan); |
674 | __FORTIFY_INLINE void *memscan(void * const POS0 p, int c, __kernel_size_t size) |
675 | { |
676 | const size_t p_size = __struct_size(p); |
677 | |
678 | if (__compiletime_lessthan(p_size, size)) |
679 | __read_overflow(); |
680 | if (p_size < size) |
681 | fortify_panic(FORTIFY_FUNC_memscan, FORTIFY_READ, p_size, size, NULL); |
682 | return __real_memscan(p, c, size); |
683 | } |
684 | |
685 | __FORTIFY_INLINE __diagnose_as(__builtin_memcmp, 1, 2, 3) |
686 | int memcmp(const void * const POS0 p, const void * const POS0 q, __kernel_size_t size) |
687 | { |
688 | const size_t p_size = __struct_size(p); |
689 | const size_t q_size = __struct_size(q); |
690 | |
691 | if (__builtin_constant_p(size)) { |
692 | if (__compiletime_lessthan(p_size, size)) |
693 | __read_overflow(); |
694 | if (__compiletime_lessthan(q_size, size)) |
695 | __read_overflow2(); |
696 | } |
697 | if (p_size < size) |
698 | fortify_panic(FORTIFY_FUNC_memcmp, FORTIFY_READ, p_size, size, INT_MIN); |
699 | else if (q_size < size) |
700 | fortify_panic(FORTIFY_FUNC_memcmp, FORTIFY_READ, q_size, size, INT_MIN); |
701 | return __underlying_memcmp(p, q, size); |
702 | } |
703 | |
704 | __FORTIFY_INLINE __diagnose_as(__builtin_memchr, 1, 2, 3) |
705 | void *memchr(const void * const POS0 p, int c, __kernel_size_t size) |
706 | { |
707 | const size_t p_size = __struct_size(p); |
708 | |
709 | if (__compiletime_lessthan(p_size, size)) |
710 | __read_overflow(); |
711 | if (p_size < size) |
712 | fortify_panic(FORTIFY_FUNC_memchr, FORTIFY_READ, p_size, size, NULL); |
713 | return __underlying_memchr(p, c, size); |
714 | } |
715 | |
716 | void *__real_memchr_inv(const void *s, int c, size_t n) __RENAME(memchr_inv); |
717 | __FORTIFY_INLINE void *memchr_inv(const void * const POS0 p, int c, size_t size) |
718 | { |
719 | const size_t p_size = __struct_size(p); |
720 | |
721 | if (__compiletime_lessthan(p_size, size)) |
722 | __read_overflow(); |
723 | if (p_size < size) |
724 | fortify_panic(FORTIFY_FUNC_memchr_inv, FORTIFY_READ, p_size, size, NULL); |
725 | return __real_memchr_inv(s: p, c, n: size); |
726 | } |
727 | |
728 | extern void *__real_kmemdup(const void *src, size_t len, gfp_t gfp) __RENAME(kmemdup) |
729 | __realloc_size(2); |
730 | __FORTIFY_INLINE void *kmemdup(const void * const POS0 p, size_t size, gfp_t gfp) |
731 | { |
732 | const size_t p_size = __struct_size(p); |
733 | |
734 | if (__compiletime_lessthan(p_size, size)) |
735 | __read_overflow(); |
736 | if (p_size < size) |
737 | fortify_panic(FORTIFY_FUNC_kmemdup, FORTIFY_READ, p_size, size, NULL); |
738 | return __real_kmemdup(src: p, len: size, gfp); |
739 | } |
740 | |
741 | /** |
742 | * strcpy - Copy a string into another string buffer |
743 | * |
744 | * @p: pointer to destination of copy |
745 | * @q: pointer to NUL-terminated source string to copy |
746 | * |
747 | * Do not use this function. While FORTIFY_SOURCE tries to avoid |
748 | * overflows, this is only possible when the sizes of @q and @p are |
749 | * known to the compiler. Prefer strscpy(), though note its different |
750 | * return values for detecting truncation. |
751 | * |
752 | * Returns @p. |
753 | * |
754 | */ |
755 | /* Defined after fortified strlen to reuse it. */ |
756 | __FORTIFY_INLINE __diagnose_as(__builtin_strcpy, 1, 2) |
757 | char *strcpy(char * const POS p, const char * const POS q) |
758 | { |
759 | const size_t p_size = __member_size(p); |
760 | const size_t q_size = __member_size(q); |
761 | size_t size; |
762 | |
763 | /* If neither buffer size is known, immediately give up. */ |
764 | if (__builtin_constant_p(p_size) && |
765 | __builtin_constant_p(q_size) && |
766 | p_size == SIZE_MAX && q_size == SIZE_MAX) |
767 | return __underlying_strcpy(p, q); |
768 | size = strlen(q) + 1; |
769 | /* Compile-time check for const size overflow. */ |
770 | if (__compiletime_lessthan(p_size, size)) |
771 | __write_overflow(); |
772 | /* Run-time check for dynamic size overflow. */ |
773 | if (p_size < size) |
774 | fortify_panic(FORTIFY_FUNC_strcpy, FORTIFY_WRITE, p_size, size, p); |
775 | __underlying_memcpy(p, q, size); |
776 | return p; |
777 | } |
778 | |
779 | /* Don't use these outside the FORITFY_SOURCE implementation */ |
780 | #undef __underlying_memchr |
781 | #undef __underlying_memcmp |
782 | #undef __underlying_strcat |
783 | #undef __underlying_strcpy |
784 | #undef __underlying_strlen |
785 | #undef __underlying_strncat |
786 | #undef __underlying_strncpy |
787 | |
788 | #undef POS |
789 | #undef POS0 |
790 | |
791 | #endif /* _LINUX_FORTIFY_STRING_H_ */ |
792 | |